Cataract extraction is one of the most commonly performed surgical procedures in the world. A cataract is formed by opacification of the crystalline lens or its envelope—the lens capsule—of the eye. The cataract obstructs passage of light through the lens. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may be increased, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract formation typically progresses slowly resulting in progressive vision loss. Cataracts are potentially blinding if untreated.
A common cataract treatment involves replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Presently, an estimated 15 million cataract surgeries per year are performed worldwide. The cataract treatment market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical maneuvers, and disposable instrumentation including ultrasonic phacoemulsification tips, tubing, various knives, and forceps.
Presently, cataract surgery is typically performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole is formed in the anterior side of the lens capsule. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye through a small incision. Typically, the IOL is held in place by the edges of the anterior capsule and the capsular bag. The IOL may also be held by the posterior capsule, either alone or in unison with the anterior capsule. This latter configuration is known in the field as a “Bag-in-Lens” implant.
One of the most technically challenging and critical steps in the cataract extraction procedure is providing access to the lens nucleus. The manual continuous curvilinear capsulorhexis (CCC) procedure evolved from an earlier technique termed can-opener capsulotomy in which a sharp needle was used to perforate the anterior lens capsule in a circular fashion followed by the removal of a circular fragment of lens capsule typically in the range of 5-8 mm in diameter. The smaller the capsulotomy, the more difficult it is to produce manually. The capsulotomy facilitates the next step of nuclear sculpting by phacoemulsification. Due to a variety of complications associated with the initial can-opener technique, attempts were made by leading experts in the field to develop a better technique for removal of the anterior lens capsule preceding the emulsification step.
The desired outcome of the manual continuous curvilinear capsulorhexis is to provide a smooth continuous circular opening through which not only the phacoemulsification of the nucleus can be performed safely and easily, but also to provide for easy insertion of the intraocular lens. The resulting opening in the anterior capsule provides both a clear central access for tool insertion during removal of the nucleus and for IOL insertion, a permanent aperture for transmission of the image to the retina of the patient, and also support of the IOL inside the remaining capsule that limits the potential for dislocation.
Furthermore, IOLs that engage the posterior capsule can benefit from a posterior capsulotomy. An example of such an IOL that can benefit from a posterior capsulotomy is described in U.S. Pat. Appl. No. 2008/0281413, entitled “METHOD AND APPARATUS FOR CREATING INCISIONS TO IMPROVE INTRAOCULAR LENS PLACEMENT”, in the name of Culbertson, et al., the entire disclosure of which is incorporated herein by reference. Such lenses may further benefit from seating the IOL in both the anterior and posterior capsule in order to best provide for accommodative motion via the zonular process. Creating a posterior capsulotomy, however, may require the surgeon to engage the vitreous and its anterior hyaloid surface. Unfortunately, the anterior hyaloid surface may be violated during the posterior capsulotomy procedure. It is postulated that a broken anterior hyaloid surface may allow anterior movement of proteins and macromolecules from the vitreous gel, which may result in fluid shifting within an already syneretic vitreous cavity. This anterior movement of proteins and macromolecules may lead to increased peripheral retinal traction and break formation. Even with an intact anterior hyaloid surface, a rent in the posterior capsule disrupts the physical barrier between the anterior and posterior segments of the eye similar to that of the aphakic eye after intracapsular lens extraction. The loss of this barrier may facilitate diffusion of hyaluronic acid, a stabilizer of the vitreous gel, into the anterior chamber; this situation may manifest clinically as collapse of the vitreous gel.
Accordingly, improved methods, techniques, and an apparatus are needed to perform an accurate posterior capsulotomy with reduced risk of compromising the anterior hyaloid surface.